A pressing apparatus for forming a corrugated foil for a foil-type fluid bearing by allowing a band-shaped metal plate to bite into between a pair of gears is described in U.S. Pat. No. 4,295,689. A pressing apparatus is described in Japanese Patent Application Laid-open No. 7-88564, which is designed to press a metal plate into a corrugated shape and bend it by forming a first groove in a lengthwise central portion of the metal plate by a central piece of a lower die and a central piece of an upper die and further forming a pair of second groove on opposite sides of such groove by two sets of the lower and upper die end pieces.
In the apparatus described in U.S. Pat. No. 4,295,689, corrugated plates having various shapes can be formed only by exchanging the gears. However, this pressing apparatus suffers from a problem that it is necessary to fabricate the gears in correspondence to a required shape of a corrugated plate, resulting in an increase in cost. Moreover, the following problem arises: the spring-back of the metal plate is liable to occur, and the dimensional accuracy of the corrugated plate is lower because the corrugated shape is formed only by the meshing of the gears, and the dimensional accuracy of the corrugated shape formed with the working accuracy of the individual tooth of the gear is dispersed.
In the apparatus described in Japanese Patent Application Laid-open No. 7-88564, when the first groove is formed in the lengthwise central portion of the metal plate by the central piece of the lower die and the central piece of the upper die, portions of the metal plate on opposite sides of the central portion are fed into the first groove, but when the second grooves are formed on the opposite sides of the first groove by the lower and upper die end pieces, a portion of the metal portion on the side of the first groove retained by the central pieces of the lower and upper dies cannot be fed into the second groove. Therefore, there is a problem that the spring-back amounts are not regular between the central portion of the metal plate and the portions on the opposite sides thereof, and when the continuous corrugated plate is formed, the working accuracy is lowered.